[PATCH v5 08/17] iommu/arm-smmu-v3: Do not change the STE twice during arm_smmu_attach_dev()

Jason Gunthorpe
2024-02-06T15:13:35Z

This was needed because the STE code required the STE to be in
ABORT/BYPASS inorder to program a cdtable or S2 STE. Now that the STE code
can automatically handle all transitions we can remove this step
from the attach_dev flow.

A few small bugs exist because of this:

1) If the core code does BLOCKED -> UNMANAGED with disable_bypass=false
then there will be a moment where the STE points at BYPASS. Since
this can be done by VFIO/IOMMUFD it is a small security race.

2) If the core code does IDENTITY -> DMA then any IOMMU_RESV_DIRECT
regions will temporarily become BLOCKED. We'd like drivers to
work in a way that allows IOMMU_RESV_DIRECT to be continuously
functional during these transitions.

Make arm_smmu_release_device() put the STE back to the correct
ABORT/BYPASS setting. Fix a bug where a IOMMU_RESV_DIRECT was ignored on
this path.

As noted before the reordering of the linked list/STE/CD changes is OK
against concurrent arm_smmu_share_asid() because of the
arm_smmu_asid_lock.

Tested-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Moritz Fischer <moritzf@google.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 1138e868c4d73e..340f3dc82c9ce0 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -2562,7 +2562,6 @@ static void arm_smmu_disable_pasid(struct arm_smmu_master *master)
static void arm_smmu_detach_dev(struct arm_smmu_master *master)
{
unsigned long flags;
- struct arm_smmu_ste target;
struct arm_smmu_domain *smmu_domain = master->domain;

if (!smmu_domain)
@@ -2576,11 +2575,6 @@ static void arm_smmu_detach_dev(struct arm_smmu_master *master)

master->domain = NULL;
master->ats_enabled = false;
- if (disable_bypass)
- arm_smmu_make_abort_ste(&target);
- else
- arm_smmu_make_bypass_ste(&target);
- arm_smmu_install_ste_for_dev(master, &target);
/*
* Clearing the CD entry isn't strictly required to detach the domain
* since the table is uninstalled anyway, but it helps avoid confusion
@@ -2928,9 +2922,18 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
static void arm_smmu_release_device(struct device *dev)
{
struct arm_smmu_master *master = dev_iommu_priv_get(dev);
+ struct arm_smmu_ste target;

if (WARN_ON(arm_smmu_master_sva_enabled(master)))
iopf_queue_remove_device(master->smmu->evtq.iopf, dev);
+
+ /* Put the STE back to what arm_smmu_init_strtab() sets */
+ if (disable_bypass && !dev->iommu->require_direct)
+ arm_smmu_make_abort_ste(&target);
+ else
+ arm_smmu_make_bypass_ste(&target);
+ arm_smmu_install_ste_for_dev(master, &target);
+
arm_smmu_detach_dev(master);
arm_smmu_disable_pasid(master);
arm_smmu_remove_master(master);
--
2.43.0